Sources of fresh water are often contaminated with disagreeable suspended solids and/or harmful pathogens including parasites such as schistosoma, cysts such as Giardia, bacteria such as cholera and viruses such as hepatitis.
Various methods are available for producing potable water from fresh water sources contaminated with suspended solids and/or pathogens. Selection of the most appropriate method requires assessment and balancing of the output requirements of the system, energy availability, and size restrictions.
One of the more constraining situations in the design of a purification system is the design of a readily transportable system capable of microbiologically purifying water contaminated with both larger pathogens such as cysts, which can be as large as about 6 microns in diameter and substantially resistant to chemical disinfection, and smaller pathogens such as viruses, which can be as small as about 0.05 microns in diameter and extremely difficult to remove by filtration.
One method employed to microbiologically purify contaminated water attempts to chemically disinfect the water by dissolving a biocide into the water or percolating the water through a biocidally active porous resin. Exemplary of the chemical disinfection method are U.S. Pat. Nos. 4,151,092 and 4,298,475.
U.S. Pat. No. 4,151,092, issued to Grimm et al., discloses a portable water purification system that includes (i) a supply of biocidally effective tablets, (ii) a first container for retaining a supply of contaminated water treated with the biocide disinfectant, (iii) a second container sealingly receivable within the first container for exerting pressure upon the treated water contained within the first container when forced downward into the first container, and (iv) a replaceable filter cartridge coupled to the base of the second container for filtering the treated water retained within the first container as the water is forced from the first container into the second container. The filter cartridge includes a polyethylene filter to remove suspended solids, a layer of activated carbon to remove the biocide and other distasteful contaminants, and a layer of felt to retain the activated carbon. While generally effective, chemical disinfection requires that the contaminated water be treated for upwards of thirty minutes with the biocide prior to removal of the biocide by passage through the activated carbon and/or consumption of the water.
U.S. Pat. No. 4,298,475, issued to Gartner, discloses a disposable, portable water purification system operable by mouth suction which comprises a straw sequentially containing filter media for removing suspended solids from the water, biocidally active anion exchange resin for chemically disinfecting the water, filter media for further removing suspended solids, activated carbon for removing distasteful contaminants including residual disinfecting chemical, and filter media for retaining the activated carbon. Gartner does not discuss the pore sizes of the filter medias.
A second method employed to microbiologically purify contaminated water attempts to filter the pathogens from the contaminated water by employing a filter having a pore size effective to remove all pathogens. While this method can be effective for removing the larger pathogens such as cysts and bacteria, such systems are generally ineffective for removing the smaller pathogens such as viruses, require significant operating energy, produce modest quantities of filtered water, and require frequent filter replacement.
U.S. Pat. Nos. 492,161, 1,130,725 and 1,510,863 disclose cleanable filtration systems which include a filter media and manually operable brushes for scrubbing the surface of the filter media in contact with the contaminated water. However, these cleanable filtration systems are not designed for use in a portable system as they rely upon a source of pressurized water.
Accordingly, a substantial need exists for a simple and efficient, manually operable, portable, water purification system that can produce significant quantities of microbiologically purified water with minimal effort and includes a means for efficiently cleaning the filter media so as to increase the useful life of the system without replacing the filter.